1. Field of the Invention
This invention relates to an electrophotographic reproducing apparatus, and more particularly to a cleaning device for removing residual toner particles from the surface of a biased transfer roll (BTR).
2. Description of Related Art
Typical cleaning methods in electrophotographic applications such as xerography have included wiping with a fur brush or web and the like, a method using magnetism or a magnetic brush, a method using an air flow and/or combination of at least several of the above.
For example, a BTR cleaning apparatus 2 known in the art is depicted in FIG. 1 and includes a cleaner housing 43 with upstream and downstream air inlets 40. To be effective, such a brush cleaner must balance the air flows from the two sides of the housing 43. This is typically done by controlling the cleaner housing 43 spacing to the BTR 20, the spacing between the brush 3 and the cleaner housing inner wall 35 and/or by adding interferences 39 between the brush 3 and the cleaner housing inner wall 35 near an air inlet 40 to create a pressure situation which will effect the air flow (air flow direction indicated at arrow 11). A flicker bar 37 is provided to help knock the toner particles free of the brush 3 fibers. Thus, the brush 3 removes toner from the BTR 20 and the airflow detones the brush fibers.
The main disadvantages of the prior art device discussed above include large size, insufficient component life, BTR surface abrasion and high unit manufacturing costs.
Notably, cleaning devices employing a metal or polymeric blade to clean residual toner from the surface of a BTR have not been forthcoming in the art, due to concern that the metal blade in particular, might damage the BTR surface. Unfortunately, polymeric blade cleaning suffers from certain deficiencies as well, primarily resulting from the frictional sealing contact which must be maintained between the blade and the surface to be cleaned. Modern high volume BTR's, however, are made of hard and smooth materials, less susceptible to blade damage, as will be discussed below. Importantly, BTR's with hard and smooth surfaces are essential for use with the cleaning apparatus described herein.
Conversely, blades have been used to clean toner retentive imaging surfaces, such as photoreceptors in electrophotographic devices, for some time. For instance, the use of lubricated metal cleaning blades for cleaning a charge retentive or photoreceptor surface is described in U.S. Pat. No. 4,970,560, to Lindblad et al. Also, Xerox Disclosure Journal, Vol. 1, No. 4, April 1976, page 79, "Impregnated Poromeric Material Cleaning Blade", by P. Spencer and D. Fisher, suggests that a poromeric structure, such as a composite of polyester fibers bound together in polyurethane, may be impregnated with a lubricant, while Xerox Disclosure Journal, Vol. II, No. 5, September/October 1977, page 107, "Lubricantless Doctor Blade for Cleaning Electrostatographic Imaging Surfaces", by S. Strella, suggests to add a thin metal or plastic shim to the cleaning edge of an elastomeric blade to reduce blade wear and tuck unders, while enhancing blade cleaning performance.
Thus, it is important, for purposes of this invention, to clearly describe the general BTR function in the electrophotographic apparatus. Paper, to which the image is to be transferred, is fed into a nip formed by the BTR and the imaging surface, or photoreceptor. The BTR is rotated at the same speed and in the same direction as the photoreceptor so that no relative motion between the paper and the untransferred toner image occurs. A commonly used BTR consists of an aluminum core with a slightly conductive urethane rubber coating. A high bias is applied to the BTR core which creates an electric field at the paper thereby causing the charged toner particles to transfer from the photoreceptor surface to the paper. The advantage of using the BTR over corona transfer method is that the pressure created in the BTR nip flattens out any ripples or other perturbations in the paper which create gaps between the paper and the photoreceptor. Gaps increase the strength of the field needed to transfer toner to the paper and cause imperfections in the resulting copies. The same gaps can be caused by large particles, such as carrier beads or toner agglomerates from the developer housing. These create "tent" deletions which appear as white circles around the large particles. BTR's can improve the appearance of copies by greatly decreasing the diameter of the "tent" deletions.
Additionally, and perhaps most notably with respect to this invention, there is a need to clean the BTR surface because paper fibers from the backside of copy sheets can be attracted to the BTR and toner which occurs on the photoreceptor surface between the copy regions will also transfer to the BTR. This toner consists of low lever "background" toner, toner developed as a control patch used in maintaining the proper toner concentration and development field in the developer housing, and/or toner which accumulates on the lapped seam of the photoreceptor belt. If these materials are not cleaned from the BTR surface, they may retransfer to the back of copy sheets, appearing as spots and smudges, and if duplexed copies are being run, the spots and smudges will appear on both sides of the copies.